The present invention relates to a processing apparatus and method for subjecting an object, such as a semiconductor wafer or the like, to a series of processes including application of processing solution, exposure and development.
During the manufacture of semiconductor devices, a circuit pattern is formed by so-called photolithography techniques whereby, after a predetermined film is formed on a semiconductor wafer which is a substrate to be processed, photoresist solution is applied to the wafer to form a resist film thereon, and a predetermined region of the resist film corresponding to the circuit pattern is exposed to light, followed by development.
Conventionally, a series of processes including photoresist coating and development is carried out by a coating-development processing system having different process units incorporated therein. This system includes process units for performing respective processes such as washing, photoresist coating, exposure, development, etc., and a cassette station having a plurality of cassettes placed thereon. The system is also provided with an interface to which an exposure unit is connected.
In the system like this, a semiconductor wafer is taken out of a cassette and transported to a process section by a transport mechanism, and in the process section, the semiconductor wafer is conveyed to and from the individual process units by a main transport mechanism.
The coating-development process is extremely important for high integration of semiconductor devices, and in the case of highly integrated devices such as 64 MB to 256 MB DRAMs, for example, conventional resists do not satisfy the requirements, and thus a chemically amplified resist, which permits formation of finer patterns, needs to be used.
However, the chemically amplified resist is heavily dependent on environment, and if alkaline components, for example, ammonia or organic amines such as NMP (N-methylpyrrolidone), exist in the atmosphere, the resolution is liable to lower. Specifically, in the step of performing a development by supplying developer to the exposed surface of the semiconductor wafer, the circuit pattern formed on the surface of the semiconductor cannot have an accurate wiring width, resulting in rising a problem that high integration cannot be achieved.
Alkaline components, which are a cause of low resolution, are present in the atmosphere because of the use of ammonia in a cleaning fluid for removing fine particles etc. adhering to the surface of an unprocessed semiconductor wafer, the use of an amine solvent as a solvent in a hydrophobic treatment performed on the surface of the semiconductor wafer prior to the step of coating resist solution to the surface of the semiconductor wafer, and the use of an amine solvent in an antireflection film coated to the semiconductor wafer to prevent abnormal exposure during the exposure step. Accurate wiring width is not achieved presumably because such alkaline components flow into the atmosphere for the heating step or the developing step following the exposure step. As a result, a reduction in the yield of IC devices the is caused.
To eliminate the adverse influence of alkaline components, the process units of the coating-development system are placed inside a housing. Air in the housing is forcibly discharged, and a chemical filter, for example, is arranged at an air inlet port which is located at an upper portion of the housing for admitting air to the process units, so as to minimize impurities such as alkaline components which are contained in the air supplied to the interior of the system and which lower the resolution.
However, the capacity of the chemical filter is limited, and if the filter deteriorates, then it is impossible to effectively remove impurities that lower the resolution. As a result, the concentration of resolution-lowering impurities in the individual process units exceeds an allowable value, lowering the yield of IC devices. Therefore, the chemical filter needs to be replaced at appropriate intervals of time, and to this end, a method is employed wherein the atmosphere in each of the process units inside the housing is sampled to measure the concentration of resolution-lowering impurities. With this method, however, the concentration detection requires much time, and thus in the aforementioned system for continuously processing semiconductor wafers, it is inevitable that the system is operated for a long time with a deteriorated chemical filter attached, resulting in a problem of reduction in the yield and reliability of the devices.